1. Field of the Invention
The present invention relates to electric motors having an armature core with electric wires wound therearound, a commutator and a neck positioned between the armature core and the commutator.
2. Description of the Related Art
In general, as schematically shown in FIG. 2(B), a rotor R of an electric motor M includes an armature core 10 with wires W wound therearound, a commutator 12 connected to the wires W, and a neck 14 positioned between the armature core 10 and the commutator 12. In order to prevent the wires W from floating up in the region of the neck 14 after the winding operation of the wires W, Japanese Laid Open Patent Publication No. 10-210704 has proposed the following process.
Thus, as shown in FIG. 10(A), in the case of a wire W1 that has one end connected to a commutator segment No. 1 of the commutator 12, the wire W1 is wound around the neck 14 by about one turn, passed through one of armature slots 11 (armature slot No. 1) formed in the outer circumferential surface of the armature core 10, and is then passed through a armature slot No. 8 that is positioned on the side opposite to the armature slot No. 1 with respect to the center of the armature core 10. Thereafter, the wire W1 is wound around the armature core JO through the armature slot No. 1 and the armature slot No. 8. After the wire W1 has wound around the armature core 10, the other end of the wire W1 leaves from the armature slot No. 8, wound around the neck 14 by a half turn, and is thereafter connected to a commutator segment No. 2 that is positioned next to the commutator segment No. 1.
The opposite ends of the wire W1 are loosely wound around the neck 14. Therefore, it is possible to prevent the wire W1 from floating in a region of the neck 14 after the winding operation of the wire W1 has been completed. In other words, the portions of the wire W1 extending between the armature core 10 and the commutator 12 do not need to be tensioned. Hence, no excessive load may be applied to the wire W1 due to excessive tension applied during the winding operation or due to vibrations that may be applied to the wire W1 during the operation of the motor. Therefore, it is possible to prevent potential breakage of the wire W1 at a position proximal to the commutator 12. In FIG. 10(A), the rotor R has sixteen armature slots and thirty two commutator segments.
FIG. 10(A) also shows a wire W2 indicated by dotted lines. The wire W2 is connected between a commutator segment No. 17 and a commutator segment No. 18 that are offset by an angle of 180° from the commutator segment No. 1 and the commutator segment No. 2, respectively. The wire W2 is wound around the armature core 10 through a armature slot No. 16 and a armature slot No. 9 in a manner similar to the wire W1. Similarly, the other wires (not shown) also are wound around the armature core 10 through the armature slots determined based on the positions of the commutator segments to which the wires are connected.
As noted above, in the above publication, the wires W1 and W2 connected to the corresponding commutator segments are wound around the armature core 10 after they have been wound about the neck 14 by about one turn. Therefore, the wires W1 and W2 may contact each other in the region of the neck 14, because the wires W1 and W2 are connected to the commutator segment No. 1 and the commutator segment No. 17, respectively, which are offset by an angle of 180° relative to each other.
As shown in FIG. 10(B), brushes Br are connected between the commutator segments No. 1 and No. 2 and between the commutator segments No. 17 and No. 18. Therefore, a voltage that is equal to a power source voltage can be applied between the wire W1 and the wire W2. Further, portions of the wires W1 and W2 positioned in the region of the neck 14 are not so firmly fixed in position in comparison with their portions positioned in the region of the armature slots 11. Therefore, there may be a possibility that the wires W1 and W2 are rub each other due to vibrations during the operation of the motor M. This may cause reduction in thickness of insulation layers of the wires W1 and W2. In particular, in the case of the wires W1 and W2, there is a possibility of causing short-circuiting, because the potential difference between the wires W1 and W2 is large.
Therefore, there is a need in the art for motors that can prevent or reduce potential short-circuiting of wires at a region of a neck.